This invention relates to centrifugal blowers, specifically an improved belt system for the connection of three phase electric motors to such blowers.
Centrifugal blowers such as those manufactured by Paxton Products Incorporated of Camarillo, Calif., are commonly driven by two pole, three phase electric motors. Such motors are powered by three electrical conductors and can run in either direction. The direction of rotation is determined by the phase sequence of the conductors attached to the motor. It is the general practice in a new installation, to attach the three conductors randomly, and then bump start the motor to determine the direction of operation. Fifty percent of the time the motor is found to run backwards, and two wires must be switched to obtain the proper operation.
On some newer belt driven blowers, a spring loaded idler pulley has been added. While this idler provides a more stable belt tension, it also adds a new vulnerability to reverse operation. If the motor is started in reverse, the idler pulley that is normally on the slack side, is now on the taut side, and is thrown violently and repeatably against whatever cover or stop it encounters. Substantial damage can occur to the pulley, the spring and to the belt. For this reason, some of the new spring loaded belt systems, are shipped with the belt not yet installed. This is a substantial inconvenience to the customer.
Even after successful initial installation, this vulnerability to reverse operation remains. Reverse operation can occur when a circuit breaker or junction box is replaced. In one case, all of the three phase motors in a factory reversed their operation, when the cables into the factory where accidentally reversed.
The current invention eliminates this vulnerability. When reverse operation occurs, a controlled automatic disconnection of the belt system results. This allows the blowers to be shipped from the factory fully assembled. It provides a visual indication of when disconnection has occurred, and a quick means of resetting the belt system without removing the cover. This protection against reverse operation remains through the life of the blower.
Replacing a belt on prior art spring loaded belt systems requires simultaneously deflecting the spring loaded idler while manipulating the belt off the pulleys. The current invention provides for quicker, easier, and safer belt changes.